So let’s begin with optical instruments. In this video we will discuss about many instruments, mainly optical microscope. Telescope is mainly of two types,

Terrestrial telescope

Astronomical telescope

We will even learn about eye too. In the above physics video, we have a diagrammatic representation of the eye. The light enters via the cornea of the eye. Behind the cornea, a fluid is filled and is called aqueous humor. The light enters via a small hole called the pupil. The brown part is iris. If there is dim light then the iris decreases in size and pupil increases in size and vice versa for bright light. Then there is a crystalline soft part called lens, near to are the ciliary muscles. These muscles exert pressure on the lens; the radius of curvature of the lens can be adjusted. If the ciliary muscles are relaxed then the focal length increases and power decreases and if stressed then the focal length decreases and the power increases. The part where light focuses is called retina. The image formed on the retina is due to optic nerves and transmits it to the brain where the image is formed. There is a liquid near it and it is known as vitreous humor. Ciliary muscles try to focus on the retina.

The last topic in this video lecture of physics is the least distance of distinct vision. It is denoted using D. Our eye focuses the light on the retina. If the light is coming from a far distance then the eye lens can focus it easily on the retina. If it’s coming from a near then, the focus is not formed. There is a certain distance near our eye up to which we can see and this is known as the least distance of distinct vision. It is 25 cm for a healthy adult eye.